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When it comes to speaking their first "words," baby Giant South American river turtles are astonishingly precocious, a new study shows.

The turtles start talking to each other even before they hatch from their eggs, Brazilian biologist Camila Ferrara discovered when she put microphones up to them, just in case, during a study on turtle vocalizations.

"I didn't expect to hear sounds inside the eggs," she recalled in an interview with Laura Lynch, guest host of CBC's As It Happens. "It was a big surprise to me."

Ferrara is an aquatic turtle specialist with the Brazil Program of the Wildlife Conservation Society, a non-profit group based at the Bronx Zoo in New York that runs conservation programs in 60 countries around the world.

She spent three years recording the sounds made by giant South American river turtles along the Trombetas River in the Amazon River Basin, which can grow to be up to 80 centimetres long – more than double the length of the common snapping turtle.

Camila Ferrara spent three years recording the sounds made by giant South American river turtles - and their eggs - along the Trombetas River in the Amazon River Basin. (Camila Ferrara/Wildlife Conservation Society Brazil)

Ferrera started by recording the sounds made by adult females that migrate in groups of up to 300 to nesting sites on the beach.

"We believe when they start to migrate, they start to call the other turtles and say 'Let's go, let's go, it's the time,'" Ferrera said.

Then she recorded the sounds made by the nesting females and by the nestlings after they hatched. Then she started to wonder how soon the turtles started to produce sounds, which led her to record the eggs.

She discovered that the baby turtles started talking up to three days before hatching, Ferrara and her collaborators reported in the journal Herpetologica.

The researchers think the turtles communicate in order to co-ordinate hatching, which takes place 45 to 50 days after the eggs are laid. That provides safety in numbers from predators.

Parenting behaviour

Ferrera started by recording the sounds made by adult female giant South American river turtles that migrate in groups of up to 300 to nesting sites on the beach. (C. Ferrara/Wildlife Conservation Society)

Ferrara said the extra volume provided by many voices together may help their mothers hear them.

The mother turtles respond to the hatchlings, and the researcher think they may be guiding their babies to the water. When that communication was reported by the researchers in 2012, it was the first time scientists had observed parenting behaviour in turtles.

Tracking studies show that the hatchlings travel with their mothers for more than two months after hatching, the Wildlife Conservation Society said in a news release.

Ferrara said the researchers are now doing further study to try to figure out what the turtles are saying and when they start talking like adults instead of babies.